KR101015088B1 - DEOXIDIZE PdO THIN FILMS USED FOR HIGH SENSITIVE SENSORS AND MANUFACTURING METHOD THEREOF - Google Patents

Abstract

The present invention includes the steps of artificially preparing a PdO thin film using a reactive DC magnetron sputtering system, and obtaining a Pd thin film having nanocracks formed by reducing the PdO thin film. .

The Pd thin film on which the nanocracks are formed has an improved hydrogen detection property and is suitable for use in a hydrogen detection sensor.

PdO thin film, sputtering, hydrogen sensor, reduction reaction

Description

Reduced PDO thin films used in ultra-high sensitivity hydrogen sensors and methods for manufacturing them {DEOXIDIZE PdO THIN FILMS USED FOR HIGH SENSITIVE SENSORS AND MANUFACTURING METHOD THEREOF}

The present invention relates to a Pd thin film, and more particularly to a Pd thin film used for detecting hydrogen.

At present, there are active researches to use hydrogen as a fuel worldwide, and hydrogen is recognized as the most important alternative energy of the future.

By the way, since hydrogen is easily diffused through most materials, it is difficult to store in a specific container, which is likely to leak. Hydrogen also has a high risk of explosion, making it difficult to use as an energy source unless it is clearly managed. Therefore, there is a need for the development of a hydrogen gas detection sensor that can detect the leakage of hydrogen.

As the hydrogen gas detection sensor, a Pd thin film sensor, a carbon nanotube sensor, a titania nanotube sensor, or the like is used. Among them, a hydrogen gas detection sensor using a Pd thin film is commonly used because of its excellent hydrogen detection capability compared to a sensor manufactured using other materials.

However, in order to fabricate a hydrogen gas detection sensor with improved performance using the Pd thin film, it is necessary to improve conditions such as reactivity with hydrogen, linearity with respect to hydrogen concentration, reaction time, and measurable concentration range. There is a need.

Accordingly, the present inventors have come up with a way to improve the hydrogen reaction characteristics and sensitivity of the Pd thin film used for the hydrogen sensor.

The present invention is to solve the above problems, the present invention is characterized in that the PdO thin film is reduced to obtain a Pd thin film.

Specifically, the PdO thin film is characterized by obtaining a Pd thin film in which nanocracks are formed through a reduction reaction with hydrogen.

Method for producing a Pd thin film according to the present invention, the Pd thin film used to detect the hydrogen, manufacturing a PdO thin film; And reacting the PdO thin film with hydrogen to produce a Pd thin film, wherein the PdO thin film is manufactured by a reactive sputtering method, and the Pd thin film is characterized in that nanocracks are formed.

In addition, the Pd thin film according to the present invention is a Pd thin film used to detect hydrogen, the Pd thin film is characterized in that the nano-cracks are formed, the Pd thin film is obtained through the reduction reaction of the PdO thin film and hydrogen. .

In the Pd thin film formed by the present invention, the nanocracks are generated to increase the exposure area / volume ratio, thereby increasing the surface area of the Pd thin film that can react with hydrogen, thereby increasing the area capable of absorbing hydrogen, thereby increasing the area of the conventional pure Pd thin film. There is a technical advantage in that it has much improved reactivity than reactivity.

The object of the present invention described above will become more apparent from the preferred embodiments of the present invention described below with reference to the accompanying drawings, by those skilled in the art. Hereinafter, the present invention will be described with reference to the accompanying drawings.

For reference, FIG. 1 shows a hydrogen reaction characteristic measuring apparatus, FIG. 2 is a surface photograph of a nano crack-formed Pd thin film, and FIG. 3 is a reaction rate of 2% hydrogen concentration of a nano crack-formed Pd thin film and a pure Pd thin film. to appear, and Figure 4 is Pd film and indicates the reactivity of the hydrogen concentration (0 to 2%) of pure Pd thin film, 5 is a PdO _1/3 (thin-film concentration of 33.3% O ₂ during production) having a nano-cracks films and PdO _1/4 (thin film concentration of 25% O ₂ during production), a thin film of hydrogen gas and showing a resistance change at the time of the reaction, 6 is PdO thin film that the concentration of O ₂ produced by different six conditions 7 shows the resistance change according to the reduction reaction of FIG. 7 shows the reactivity, reaction time, and recovery time of 2% hydrogen of the Pd thin film formed by the reduction reaction of the PdO thin film formed with different oxygen partial pressure, and FIG. 8 shows PdO5 _{5. %, 10% PdO,} PdO _{15%, 20% PdO,} PdO _{25%, 30%} reduction half of the PdO thin film After that, the device shows a photograph of a nano-cracks formed in the thin film surface.

The present invention includes the steps of artificially preparing a PdO thin film using a reactive DC magnetron sputtering system, and obtaining a reduced Pd thin film by exposing the PdO thin film to hydrogen.

In addition, to improve the characteristics of the nano-cracked thin film as described above through the experiment. (Experimental example 1, 2)

The steps for fabricating the PdO thin film of the present invention are as follows.

Reactive DC magnetron sputtering system is used to fabricate PdO thin film. That is, in order to form Pd oxide on the cleaned Si substrate, a pure Pd target is deposited at an initial base pressure of 4 × 10 ⁻⁸ Torr using a reactive sputtering technique. At this time, the PdO thin film is manufactured by controlling the flow rates of Ar gas and O ₂ gas using a mass flow controller (MFC).

Steps for manufacturing the Pd thin film of the present invention are as follows.

In order to obtain the Pd thin film by reacting the formed PdO thin film with hydrogen, the PdO thin film is placed in a hydrogen reaction characteristic measuring apparatus and subjected to a reduction process.

The hydrogen reaction characteristic measuring apparatus has the advantage of measuring the electrical characteristics while supplying hydrogen to the PdO thin film. The hydrogen reaction characteristic measuring apparatus, specifically, PdO thin film 10, the chamber 100, H ₂ and N ₂ It is configured to include a gas valve 110, a mass flow controller (MFC) 120, and a current, voltage application device 130.

The chamber 100 is actually H ₂ In order to investigate the reactivity with the gas and the electrical characteristic change of the fabricated device, it serves to create a gas atmosphere of a desired ratio, and the H ₂ and N ₂ gas valve 110 and the MFC (mass flow controller) 120 It functions to accurately control the composition and ratio of the mixed gas (H ₂ : N ₂ ) in the chamber 100, the current, voltage applying device 130 detects the electrical signal of the PdO thin film.

The reduction reaction between the PdO thin film 10 and the supplied hydrogen (H ₂ ) placed in the chamber 100 of the hydrogen reaction characteristic measurement apparatus is represented as follows.

2PdO + 2H _{2 (v)} → 2Pd + 2H ₂ O _(v)

When the PdO thin film reacts with hydrogen and is reduced to a Pd thin film, oxygen atoms of the PdO thin film meet hydrogen and generate H ₂ O (water vapor) in the form of a gas, where water vapor escapes through the surface of the PdO thin film and causes small cracks. (nano-crack) As a result of the nanocracks generated, the sensitivity to hydrogen is improved as the area / volume ratio of the Pd thin film is increased. For reference, FIG. 2 shows a surface photograph of the Pd thin film on which nanocracks are formed after the reduction reaction of the PdO thin film is finished.

However, if the nanocracks can be formed by other methods other than the formation of nanocracks due to the reduction reaction as described above, the Pd thin film may be manufactured using the method, and other materials besides the Pd thin film may be formed. By using the nano-crack formed a thin film as in the present invention can be made. In addition, the nano-cracked Pd thin film is characterized in that it can be used as a disposable hydrogen sensor.

On the other hand, the present invention looks at the change in resistance according to the oxygen partial pressure applied when the PdO thin film is manufactured by the reactive sputtering technique. That is, PdO _1/3 thin film further improved by measuring the change in resistance when the (thin-film concentration of 33.3% O ₂ during production) and PdO _1/4 (the thin film 25% O ₂ concentration in the produced) film is reacted with hydrogen gas We present a way to obtain Pd thin films. In addition, in order to further refine the experiment, the partial pressure of oxygen applied during the production of the PdO thin film was further subdivided to further refine PdO _{5 %,} PdO _{10 %,} PdO _{15 %,} PdO _{20 %,} PdO _{25 %, and} PdO _{30 %.} After the thin film was manufactured in the same manner as described above, the resistance change was measured. (Experimental Example 3)

In addition, according to the oxygen partial pressure applied when the PdO thin film is manufactured, a difference in size and density of nanocracks formed on the reduced Pd thin film surface occurs, and the size and density of the nanocracks may improve hydrogen detection characteristics. I want to prove it. Experimental Example 4

Hereinafter, with reference to the accompanying drawings an embodiment of the present invention will be described in detail. This is a preferred embodiment the present invention is not limited thereto.

Experimental Example 1

The sensitivity of hydrogen (2% hydrogen) of nano cracked Pd thin film and pure Pd thin film is examined. Here, the pure Pd thin film means a Pd thin film conventionally used, that is, not subjected to a reduction process.

Table 1 shows the numerical values relating to the resistance change and the reactivity. FIG. 3A is a reactivity of 2% hydrogen concentration of the nano-cracked Pd thin film and FIG. 3B is a reactivity of 2% hydrogen of the pure Pd thin film.

Nano crack formed Pd thin film Pure Pd Thin Film Initial resistance (R ₀ ) 4.04Ω 1.5Ω Resistance (R) 5.14Ω 2.1Ω Responsiveness (S = (RR ₀ ) / R ₀ × 100)) 27.2% 40% Reaction time 7s 27 s Recovery time 15 s 59s

Through the Table 1, the initial resistance of the nano-cracked Pd thin film in the reactivity is 4.04Ω and the maximum resistance is 5.14Ω shows a response of about 27.2%. In the case of pure Pd thin film, the initial resistance is 1.5Ω and the maximum resistance is 2.1Ω, which shows about 40% reactivity. In addition, the reaction time of the nano-cracked Pd thin film is 7 seconds and the recovery time is 15 seconds, while the reaction time of the pure Pd thin film is 27 seconds and the recovery time is 59 seconds.

Although the Pd thin film on which the nanocracks are formed has a lower reactivity than the pure Pd thin film, the time for hydrogen adsorption and desorption is reduced by about four times than that of the pure Pd thin film. This is because the exposure area / volume ratio increases as nanocracks are generated, thereby increasing the surface of the Pd thin film that can react with hydrogen and increasing the area capable of absorbing hydrogen.

Experimental Example 2

Experiments on sensitivity of hydrogen crack in Pd thin film and pure Pd thin film with nanocracks are performed.

In order to determine the sensitivity according to the hydrogen concentration, the inventors set the hydrogen concentration section of 0% to 1.5% and the hydrogen concentration section of 2% in the conventional Pd thin film and the Pd thin film in which the nanocracks are formed, and then measured the reactivity. And the same result as in FIG. 4.

Table 2 shows the state of the graph regarding the sensitivity according to the hydrogen concentration, Figure 4a is a reaction chart for the hydrogen concentration (0 ~ 2%) of the nano-cracked Pd thin film, Figure 4b is the hydrogen concentration of the pure Pd thin film (0 ~ 2%).

Nano crack formed Pd thin film Pure Pd Thin Film 0% ~ 1.25% hydrogen concentration Linear Linear 1.25% ~ 2% hydrogen concentration Linear Discontinuous resistance change

In the case of pure Pd thin films, the linear response to hydrogen concentration is shown in the hydrogen concentration range from 0 to 1.25%, but the resistance change rapidly increases in the region after 1.25%. On the other hand, in the case of the nano-cracked Pd thin film can be seen to have an overall linear slope in the hydrogen concentration range of 0 ~ 2%.

When hydrogen is adsorbed into the Pd thin film, the α phase of PdH is formed. As the concentration of hydrogen adsorbed into the Pd thin film increases, the PdH phase of the α phase changes into the β phase. Such a phase change is a major cause of increasing the resistance of the Pd thin film.

Therefore, the portion where the reactivity is rapidly increased in the pure Pd thin film in a section of 1.25% hydrogen concentration or more can be seen that all of the α-phase PdH is converted into β-phase. However, in the case of Pd thin film with nanocracks, the reactivity in the 0 ~ 2% hydrogen concentration range maintains the linear slope and does not show a large difference in resistance. It is considered to be because it prevents it.

That is, it can be seen that the nanocracked Pd thin film is suitable for use as a hydrogen sensor because the phase inversion is gradually made and the resistance is not increased.

Experimental Example 3

In order to examine the hydrogen sensitivity according to the proportion of oxygen provided in the production of PdO thin film using reactive sputtering technique, the experiment was put into a hydrogen reaction characteristic measuring apparatus.

Using MFC (mass flow controller) controlling the flow rate of the Ar gas and O ₂ gas, and making the thickness of 40nm PdO _1/3 thin film and the PdO _1/4 film. (The flow rate of Ar and O ₂ x: gives flowing at a ratio of 1, PdO deposition is completed is referred to as PdO _x% along PdO _{1 / x} d representation, or the concentration (% of O ₂₎ according to the ratio of O _2. )

In addition, the present inventors made hydrogen gas and PdO _{5 %,} PdO _{10 %,} PdO _{15 %,} PdO _20%, PdO _{25 %,} PdO _{30 %} thin film in the same manner as described above to further proceed the experiment The change in resistance during the reaction was measured.

As a result of the above, Table 3, Fig. 5, and Fig. 6 were obtained.

Table 3 shows the value of the resistance change and response, Fig 5a, 5b is _1/3 PdO thin film and the PdO _1/4 represents a thin film resistance change at the time of the hydrogen gas and the reaction, 6 is _{5% PdO,} PdO _{10 %,} PdO _{15 %,} PdO _{20 %,} PdO _{25 %,} PdO _{30 %} Thin film shows the change in resistance when reacted with hydrogen gas.

PdO _1/3 thin film PdO _1/4 films Initial resistance (R ₀ ) 230.6Ω 93.6 Ω Resistance (R) 9.6Ω 6.3Ω Reactivity (S = (RR ₀ ) / R ₀ × 100) 95.8% 93.2% Reaction time 300 s 143 s

Look through the results of Experimental Example 3, PdO response of _1/3 thin film is 95.8%, and the time it takes reduced to Pd thin film having a nano-cracks react with hydrogen to 300 seconds. PdO _{1 /} reaction of the thin film ₄ is 93.2%, and the time it takes reduced to Pd thin film having a nano-cracks react with hydrogen is 143 seconds.

In addition, as a result of examining the resistance change caused by the reaction of the six PdO thin films formed with different oxygen partial pressures with hydrogen through FIG. Can be. Therefore, it can be seen that it is desirable to produce a PdO thin film having a high oxygen partial pressure.

Experimental Example 4

When producing PdO thin film using reactive sputtering technique, 6 PdO thin films (PdO _{5 %,} PdO _{10 %,} PdO _{15 %,} PdO _{20 %,} PdO _{25 %,} PdO _{30 %} ) After fabrication, it was placed in a hydrogen reaction characteristic measuring device to test the sensitivity, reaction time, and recovery time for 2% hydrogen concentration.

As a result of the above, Figs. 7 and 8 were obtained.

FIG. 7 shows the reactivity, reaction time, and recovery time according to 2% hydrogen concentration of Pd thin film on which nanocracks are formed. FIG. 8 shows PdO _{15 %} thin film, PdO _{20 %} thin film, PdO _{25 %} thin film, and PdO _{30 %} thin film. Device photo of nano cracks formed on the surface of thin film after reduction reaction.

As shown in the results of Experimental Example 4, as shown in Figure 7, the sensitivity, reaction time, and recovery as the flow rate of oxygen provided in the production of PdO thin film under the condition that the flow rate of hydrogen and nitrogen gas by the MFC is controlled This results in an improved time. This is because the PdO thin film formed with the high oxygen partial pressure reacts with hydrogen to generate H ₂ O (water vapor), and large nano cracks are formed on the surface of the PdO thin film with high density.

Therefore, when the large sized, dense nanocracks are formed on the reduced Pd thin film surface, the sensitivity, reaction rate, and recovery rate for hydrogen are improved, and when applied to the hydrogen detection sensor, the hydrogen detection characteristics will be significantly improved. .

The foregoing description is in connection with specific embodiments, and various modifications and changes may be made without departing from the spirit and scope of the invention as indicated by the claims.

1 is a hydrogen reaction characteristic measuring apparatus

FIG. 2 is a surface photograph of a Pd thin film having nanocracks formed after a reduction reaction of the PdO thin film

FIG. 3 is a reaction diagram of 2% hydrogen concentration of Pd thin film and pure Pd thin film on which nanocracks are formed

Figure 4 is a reaction chart for the hydrogen concentration (0 ~ 2%) of the nano-cracked Pd thin film and pure Pd thin film

Figure 5 (a concentration of _{33.3% O 2) PdO 1/} 3 Measuring the resistance change of when the (concentration of 25% O ₂₎ and thin film PdO _1/4 films react with hydrogen gas

6 is a measurement of the resistance change when the PdO thin film produced according to the ratio of Ar and O ₂ reacts with hydrogen gas

7 is a reaction rate, reaction rate, recovery rate by 2% hydrogen after reduction of the PdO thin film produced according to the ratio of Ar and O ₂

8 is a device photograph of the nanocracks generated on the surface of the thin film after the reduction of PdO _{5 %,} PdO _{10 %,} PdO _{15 %,} PdO _{20 %,} PdO _{25 %,} PdO _{30 %} thin film

Claims (7)

In the Pd thin film used to detect hydrogen, Artificially preparing a PdO thin film using a reactive sputtering method; And The method of manufacturing a Pd thin film comprising the step of producing a Pd thin film with nano-cracks formed on the surface by reducing the PdO thin film by hydrogen exposure. delete delete In the Pd thin film used to detect hydrogen, The Pd thin film is a Pd thin film, characterized in that the nano-crack formed on the surface by reducing the PdO thin film by hydrogen exposure. delete The method of claim 4, wherein The nanocracks generate a difference in size and density according to the conditions of oxygen partial pressure provided when the PdO thin film is manufactured, and the increase in size and density of the nanocracks improves the performance of the hydrogen detection sensor. Pd thin film. delete

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